The main goal of a mitotic cell is to equally segregate its chromosomes and centrosomes between two daughter cells. The careful orchestration of cytoskeletal and chromosomal events requires coordinated action by members of the CDK (cyclin-dependent kinase), PLKs (polo-like kinase) and Aurora kinase families. The study of these kinases, their regulatory subunits and substrates has attracted considerable attention in recent years, in part because they are all candidate targets for cancer therapy.
During mitosis, a spectacular reorganization of the cytoskeleton occurs that builds a bipolar microtubule spindle that assures proper segregation of chromosomes and requires a number of precisely coordinated cell-cycle events to occur. Considering the complexity of mitosis, not surprisingly there are many mitotic defects that can lead to the formation of aneuploid daughter cells, i.e. cells that possess an altered content of DNA. To prevent the appearance of such aneuploid cells, the cell will enter into mitotic catastrophe, i.e. a type of cell death. Cells that fail to execute mitotic catastrophe in response to mitotic failure are likely to divide asymmetrically, with the consequent generation of aneuploid cells.
Most tumors develop in an (oligo)clonal and stochastic manner, through a multi-step process. It is accordingly a hypothesis that one of the mechanisms that contribute to oncogenesis consists of ‘cytogenetic catastrophe’, i.e. the failure to activate mitotic catastrophe in response to mitotic failure (Castedo, M., et al., Oncogene (2004) 23, 2825-2837). In these circumstances aneuploidization could result from the asymmetric division of polyploid cells, generated from an illicit cell fusion. Polyploidy is frequently observed in neoplasia and constitutes a negative prognostic factor, while aneuploidy is a near to general characteristic of cancer.
As already mentioned above, the networks of kinases that regulate the mitotic events are all candidate targets for cancer therapy. For example, Aurora A is an oncogenic serine/threonine kinase that plays a role in centrosome separation and in the formation of the mitotic bipolar spindle. Aurora B is required for chromosome alignment, kinetochore-microtubule bi-orientation, activation of the spindle assembly checkpoint and cytokinesis. Both Aurora A and B are upregulated in various cancers, Aurora A is commonly amplified in melanoma and cancers of the breast, colon, pancreas, ovaries, bladder, liver and stomach. Aurora B is frequently increased in tumors such as colorectal cancer and high-grade gliomas, and Aurora B overexpression in CHO cells results in an increased invasiveness, suggesting a role for Aurora B in tumorigenesis (Carvajal, R. D. et al., Clin. Cancer Res. (2006) 12(23), 6869-6875).
Another member of the kinases involved in cellular mitosis, are the cyclin-dependent kinases CDKs that are at the core of the machinery that drives cell division. It is for example, well established that CDK1 interacts with cyclin B1 to form an active heterodimer, the ‘mitosis-promoting factor’. The mitosis-promoting factor induces mitosis by phosphorylating and activating enzymes regulating chromatin condensation, nuclear membrane breakdown, mitosis-specific microtubule reorganization and actin cytoskeleton allowing for mitotic rounding up of the cell. Aberrant mitotic entry can result in cytogenic catastrophe as observed in many tumor cells. This requires the activation of CDK1, and it is currently assumed that premature entry of active CDK1/cyclin B1 complex into the nucleus suffices to cause premature chromatin condensation that may result in aneuploidization (Castedo M. et al., supra). It is also established that CDK4 is important for cell cycle G1 phase progression. The activity of this kinase is restricted to the G1-S phase, which is controlled by the regulatory subunits D-type cyclins and CDK inhibitor p16(INK4a). This kinase was shown to be responsible for the phosphorylation of retinoblastoma gene product (Rb). Defects in the p16/CDK4:cyclinD/Rb pathway was found to lead to tumor formation. Genetic alteration or over expression of CDK4 has also been observed in various tumor cell types. This increasing body of evidence provides a link between tumor development and CDK related malfunctions and led to an intense search for inhibitors of the CDK family as an approach to cancer therapy.
Other members of the kinases involved in cellular mitosis are Polo-like kinases (PLKs). PLKs are key enzymes that control mitotic entry of proliferating cells and regulate many aspects of mitosis (Barr, F. A. et al., Nat. Rev. Mol. Cell. Biol. 2004, 5, 429-441). Four distinct PLKs have been identified to date in mammals. Whereas PLK1, PLK2 and PLK3 are expressed in all tissues and structurally homologous in that they comprise the N-terminal catalytic kinase domain and two polo-boxes, PLK 4 differs not only in structure, compared to the other PLKs it has only one polo-box, but also in the distribution of PLK4 mRNA in adults that is restricted to certain tissues such as testes and thymus (Karn, T. et al., Oncol. Rep. 1997, 4, 505-510; Fode, C. et al., Proc. Natl. Acad. Sci. USA 1994, 91, 6388-6392). Given the established role of PLKs as mitotic regulators, they have been regarded as validated mitotic cancer targets for a number of years. For example, PLK1 when fused to an antennapedia peptide and efficiently internalized into cells caused an inhibition of cancer cell proliferation (Yuan, J., et al., Cancer Res. 62, 2002, 4186-4190), whereas downregulation of PLK1 by antisense induced the growth inhibition of cancer cells (Spankuch-Schmitt, B., et al., Oncogene 21, 2002, 3162-3171). PLK2 was recently found to be a novel p53 target gene and RNAi silencing of PLK2 leads to mitotic catastrophe in taxol-exposed cells (Burns, T F., et al., Mol Cell Biol. 23, 2003, 5556-5571). For PLK3 it was found that it induces cell cycle arrest and apoptosis through perturbation of microtubule structure (Wang, Q., et al., Mol Cell Biol. 22, 2002, 3450-3459) and PLK4 was shown to be transcriptionally repressed by p53 and induces apoptosis upon RNAi silencing (Li, J., et al., Neoplasia 7, 2005, 312-323). PLK4 was also found to be required for centriole duplication and flagella development. The absence of centrioles, and hence basal bodies, compromises the meiotic divisions and the formation of sperm axonemes (Bettencourt-Dias M., et al., Current Biology 15, 2005, 2199-2207). Thus confirming that targeting PLKs with conventional agents may be a valid and effective anticancer strategy. The involvement of PLK4 in flagella development also implies a possible use of PLK4 antagonists as male contraceptives.
Glycogen synthase kinase (GSK)-3 has also emerged as an attractive therapeutic target for the treatment of cancer. GSK-3β is a critical regulator of nuclear factor (NF)κB nuclear activity, suggesting that inhibition of GSK-3β could be effective in the treatment of a wide variety of tumors with constitutively active NFκB.
Certain macrocyclic compounds having kinase inhibitory activity have been described. WO 2004/078682 discloses cyclic compounds, pharmaceutical compositions comprising such cyclic compounds and methods of using such compounds to treat or prevent diseases and disorders associated with the activity of CDK2 and CDK5.
WO 2007/058627 discloses oxygen linked and substituted pyrimidine compounds and the uses of these compounds in the treatment of proliferative disorders as well as other disorders or conditions related to or associated with kinases.
WO 2007/058628 discloses heteroalkyl linked pyrimidine derivatives and the uses of these compounds in the treatment of proliferative disorders as well as other-conditions or disorders associated with kinases.
However, there is still a need to develop new compounds having improved pharmacological and therapeutic activities for the treatment of kinase related diseases. It is accordingly one of the objects of the present invention to provide new compounds that are kinase inhibitors and that are useful in the treatment of kinase associated diseases such as cell proliferative disorders.